1. Field of Invention
The present invention relates to an electrooptic device, a liquid crystal device, and a projection display device. More particularly, the present invention is related to the configuration of an electrooptic device, represented by a liquid crystal device or the like, that can sufficiently suppress a substrate floating effect and that is suitable for use in, for example, a projection display device.
2. Description of Related Art
Currently, SOI (Silicon on Insulator) technology, in which a semiconductor layer made of a single-crystal silicon layer is formed on an insulating layer and a semiconductor device, such as a transistor element, is formed on the semiconductor layer, has the advantages of, for example, providing high-speed devices, low power consumption, and high integration, and is applicable to, for example, electrooptic devices such as liquid crystal devices.
In a general type of bulk semiconductor device, since a channel region of an MIS (Metal-Insulator-Silicon) transistor can be maintained at a predetermined potential by an underlying substrate, the electrical characteristics, such as breakdown voltage, of the device will not be deteriorated by a parasitic bipolar phenomenon that is caused by a change in potential in the channel region, or the like. In contrast, in an SOI-MIS transistor, since the lower side of a channel region is completely isolated by an insulating underlayer, the channel region cannot be fixed at a predetermined potential, unlike in the above transistor, and is in an electrically floating state.
In this case, excess carriers are produced by impact ionization due to the impact of carriers accelerated by an electric field in the vicinity of a drain region on the crystal lattice, and are accumulated on the lower side of the channel region. When the channel potential is increased by such accumulation of excess carriers on the lower side of the channel region, a source-channel-drain NPN structure (in the case of an N channel type) works as an apparent bipolar element, and therefore, the electrical characteristics are deteriorated. For example, the source/drain breakdown voltage of the device is lowered by an abnormal current. A series of phenomena caused by the electrically floating state of the channel region are called substrate floating effects.
Accordingly, a technique has been adopted heretofore which suppresses substrate floating effects by forming a body contact region electrically connected to a channel region through a predetermined route and by extracting excess carriers accumulated in the channel region through the body contact region.
However, when a body contact region is formed in each of the MIS transistors used in an pixel region of an electrooptic device represented by a liquid crystal device or the like, the area occupied by the MIS transistors is increased, and this makes it difficult to increase the pixel density. In particular, in a transmissive liquid crystal device, the aperture ratio decreases. Also, in a peripheral driving circuit outside the pixel region, the body contact region makes high integration difficult, the peripheral portion (frame portion) of the device is enlarged, and consequently, size reduction is impossible.
In electrooptic devices used in electronic devices, such as a projection display device, when high-intensity light from a light source enters channel regions and LDD (Lightly Doped Drain) regions of pixel transistors, carriers are produced by optical excitation, charges leak from pixel storage capacitors, and this causes display unevenness such as flicker.